@model float?

@{
    float f;
    if (!Model.HasValue)
    {
        f = 0.0f;
    }
    else
    {
        f = Model.Value;
    }
}

<div class="form-group">
    @Html.LabelFor(m => m, new { @class = "control-label" })
    <div class="input-group">
        @Html.TextBox(
        "", f,
        new { @class = "form-control" })
        <span class="input-group-addon">0,00</span>
    </div>
    @Html.ValidationMessageFor(m => m, null)
</div>
